Components Development and Experimental Testing for an Onboard Liquid Hydrogen Supply and Conditioning System in High-Power Fuel Cell Aviation Applications

Expected Outcome

Cryogenically stored hydrogen is the preferred energy carrier for commercial aircraft powered by fuel cells due to its better volumetric energy density. This conditioning system connects the cryogenic hydrogen storage to all onboard propulsion and auxiliary systems, that directly consume hydrogen. However, since fuel cells require gaseous hydrogen, the hydrogen supply system should reliably evaporate hydrogen and provide stable pressure and temperature outputs across a wide range of operating conditions and varying fuel demands, during different flight phases. The system should also be capable of responding to critical scenarios, such as (partial) engine failure, ensuring continuous hydrogen supply to remaining power units. Furthermore, it should be lightweight and aerodynamically efficient, to avoid degrading performance or interfering with flight dynamics.

Such an LH2 supply and conditioning system shall be developed in cooperation between the Clean Aviation and Clean Hydrogen Joint Undertakings, requiring two projects to run in parallel and in synergy[1]. More specifically, while the Clean Aviation JU’s project will focus on creating a foundation for a certifiable hydrogen supply and conditioning system by defining system-level requirements, developing system architecture designs and carrying out system performance tests with a demonstrator system in the context of the Call Topic HORIZON-JU-CLEAN-AVIATION-2026-04-HPA-02: “Demonstration of an integrated hydrogen fuel system for a fully electric hydrogen fuel cell powered aircraft”, this topic focuses on development and testing of key specific components for LH2 supply and conditioning systems for Fuel Cells based electric propulsion such as those specified in the Scope of this topic text. While Clean Aviation is responsible for the development of the overall system architecture and the design and testing of architecture-driving components such as the LH₂ pump and heat exchanger, the Clean Hydrogen JU project focuses on the development and validation of non-architecture-driving subsystems and components. These include elements like piping, valves, sensors, and control units. Clean Hydrogen JU’s project will further contribute with simulation, analysis, and dynamic testing activities that support component development and explore synergies with other heavy-duty applications.

The project results are expected to contribute to the following outcomes:

• Paving the way to define integrable and certifiable architectures for liquid hydrogen storage, supply and conditioning systems for regional aircraft;
• Paving the way to demonstrate a flightworthy hydrogen supply and conditioning system for regional aircraft (up to 10 MW power class) using liquid hydrogen and fuel cells;
• Facilitating cross-sectoral collaboration and knowledge transfer, supporting industry-related skills and enhance awareness, acceptance and fuel cell systems uptake;
• Developing a regulatory framework for widespread use of large hydrogen cryogenic technology and fuel cell systems;

Project results are expected to contribute to the following objectives and 2030 KPIs of the Clean Hydrogen JU SRIA:

• Enabling continuous hydrogen mass flow in civil aircraft of up to 280 g/s (peak power) and 170 g/s (cruise flight) for up to 10 MW propulsive power. Depending on the system architecture the hydrogen mass flow can be provided by multiple LH2-tank and LH2 supply and conditioning systems.
• Achieving a gravimetric index above 30 % for the entire onboard fuel storage, supply and conditioning system. The defined system boundary includes the cryogenic storage tank (including stored hydrogen), piping, venting, supply and conditioning systems.
• Achieving an operational index of one aircraft-on-ground (AOG) events to a maximum of one per 3000 flight hours for the entire onboard fuel storage, supply and conditioning system.

Scope

The scope of the topic is to design, develop and demonstrate on the ground the reliable and safe operation of key components (up to TRL 5) and integrated sub-systems combining them (up to TRL 4). This includes, but is not limited, to cryogenic valves, insulation, piping, sensors, metering systems and interfaces between the tank and the fuel cell systems. The system level requirements, the preliminary system architecture and the operational envelope will be defined in coordination with the project funded under Clean Aviation JU. In return, the project that will be selected from this topic will provide feedback on component feasibility, performance, development status and deliver pre-tested components for final system integration and testing. A number of defined collaborative meetings will be held to ensure alignment between the system-level design and the component development efforts. While each project has its own deliverables, they will collaborate on integrated testing efforts, where the TRL5 components from Clean Hydrogen project are used to build and test the TRL4 system within the Clean Aviation project.

• Suitable test infrastructures should be used, for example by research institutions and the industrial sector to demonstrate respective technology readiness levels;
• Identify, under the Clean Aviation JU funded project, the scope of the components to be developed and tested;
• Derive the requirements for specific components (e.g. sensors, valves, monitoring systems) from the system definition provided in cooperation with Clean Aviation funded project. This ensures that the developed components will be compatible with the overall system architecture;
• Detailed component design of key components e.g. for the hydrogen feed and vent systems. This includes material selection, sizing, mechanical and thermal analysis;
• Manufacture and test prototype components to validate their performance, functionality and reliability in a cryogenic hydrogen environment;
• Develop and test control algorithms necessary to manage the operation of the components (e.g. valve sequencing for venting, pressure control). These algorithms are essential for safe and efficient system operation;

Simulation and experimental component analysis are needed. Simulations are intended to complement component development activities by providing tools and methods to derive control strategies, optimal operating conditions, optimise thermodynamic integration and assess performance impacts at the aircraft system level. They should include component, subsystems and system modelling (if necessary, from hydrogen onboard storage to hydrogen conversion in fuel cells), to analyse thermo-fluid-dynamic behaviour, dynamics and energy flows.

Therefore, the project should address the following:

• Development and validation of sizing- and simulation tools for hydrogen supply components design tailored to application specific requirements;
• Identification of mass sensitivity for hydrogen supply system components enabling further mass reduction. Exploration of potential indirect weight reductions in other systems by using cooling power availability during evaporation and heat up of liquid hydrogen;
• Reduction of aerodynamic drag associated with heat exchange surfaces for in-situ hydrogen evaporation. Consideration of secondary coolant specifications to optimise the heat exchanger in realistic conditions, while maximising potential use of the available cooling;
• Evaluation of component performance across all operating phases in connection with liquid hydrogen and fuel cell powertrains using simulation tools;
• Development of control strategies for the hydrogen supply and conditioning system relevant for the testing purpose as well as for an hydrogen powered aircraft[2] (HPA) mission profile;

The development of components shall be complemented by experimental system analysis - preferably at research facilities or with support from industrial partner - in combination with a high-power fuel cell system, within a relevant system architecture and power class. Leveraging available infrastructure is expected to provide operational experience under dynamic and mission-relevant conditions, allowing early identification of system-level challenges. These insights will inform and improve component-specific development beyond what could be achieved through systems engineering alone. In parallel, developed components are expected to undergo individual qualification to ensure performance and reliability. These activities contribute to establishing safe, certifiable, and aviation-ready subsystem maturity.

• Demonstrate hydrogen supply and conditioning component and sub-system operations under application relevant conditions and evaluate responses to system-level failure cases and dynamic constraints;
• Address the durability of materials, components and sub-systems under representative environmental- and mission relevant conditions, including cleanliness and fluid purity sensitivity of the components.

The component development work and the broader sub-system analysis (simulation and experimental testing) are expected to contribute to light weight, energy efficient and low-maintenance designs. The analysis should explore enabling factors (smart topologies, reduction of components & sensors) to achieve such designs, relevant but not limited to the component-level improvements. With system analysis and simulation, critical safety aspects (e.g. failure scenarios, leakage risks, purity effects) are also expected to be assessed.

Scientific analyses and innovation activities should aim to explore the scientific and technological foundations that support safe, certifiable, and high-performance hydrogen supply systems:

• Perform safety and failure mode, effects and criticality analysis in alignment with aviation standards;
• Consider safety requirements for liquid hydrogen supply components: perform review of available liquid hydrogen fueling safety knowledge, prioritise potential incident scenarios, identify and address safety knowledge gaps, propose safety solutions` strategies. Where appropriate based on engineering and development needs, complement these activities with a detailed quantitative risk analysis and derive applicable risk management measures (including safety devices);
• Enablement of robust and safe fuel cell operation in aviation environments;
• Validation of hydrogen leakage rates considering both safety and climate impact;
• Conduct scientific analyses of the potential cooling systems optimisation/reduction by using cooling power available during evaporation and heat-up of liquid hydrogen.

This project should build on insights from Clean Hydrogen JU projects such as ELVHYS[3], HEAVEN[4], BRAVA[5] and COCOLIH2T[6]. HEAVEN contributed to modular fuel cell and cryogenic storage solutions, while BRAVA sets the foundation to demonstrate a hydrogen-powered fuel cell system exceeding 2 MW (propulsive power for one out of several aircraft powertrains), highlighting the potential of hydrogen in future aircraft energy systems. COCOLIH2T aims to develop a safe composite and vacuum-insulated liquid hydrogen (LH2) tank for the aviation sector, using innovative fabrication technologies to design and manufacture a conformal tank. It should also leverage findings from the Clean Aviation JU projects HEROPS[7], NEWBORN[8], FAME[9], H2ELIOS[10], which explores the integration of liquid hydrogen and fuel cells in propulsion architectures for emission-free regional aircraft.

In order to secure the exchange of the necessary elements (such as, but not limited to, liability, background and foreground IP, hardware, digital and physical assets) and information (requirements, specifications, etc.) needed to perform the components testing activities at the TRL targets defined in this topic at project completion, the project selected under this topic will require an enhanced cooperation with the project(s) funded under the Clean Aviation topic “HORIZON-JU-CLEAN-AVIATION-2026-04-HPA-02: Demonstration of an integrated hydrogen fuel system for a fully electric hydrogen fuel cell powered aircraft”.

The project may also build on prior developments from earlier national or other European programs.

Development of cryogenic tank and fuel cell system are excluded from the scope of the topic.

Additional considerations:

• R&D activities should be scalable and transferable to aviation and potentially present positive spill-over effects with other heavy-duty applications.
• Projects should outline how the developed components - while tailored for fuel cell applications - could also enable positive spill-over effects for hydrogen combustion in aviation, supporting broader hydrogen use cases across propulsion technologies;
• Projects should justify proposed budgets based on component/system test size, test duration, and TRL objectives;
• Innovation activities should clearly define the novel aspects and demonstration scale;
• Collaboration across relevant stakeholders and end users (e.g., aircraft manufacturers, fuel cell and hydrogen technology developers, certification bodies) is encouraged;
• While formal certification is not required within this call, proposals should demonstrate how their results and activities support future certification processes and compliance with relevant aviation standards.

For additional elements applicable to all topics please refer to section 2.2.3.2.

Activities are expected to achieve TRL 5 at components level and TRL 4 for integrated subsystems by the end of the project- see General Annex B.

The JU estimates that an EU contribution of maximum EUR 8.00 million would allow these outcomes to be addressed appropriately.

Technology Readiness Level - Technology readiness level expected from completed projects

Activities are expected to achieve TRL 5 at components level and TRL 4 for integrated subsystems by the end of the project- see General Annex B.

[1] In the event that no project is selected under the related Clean Aviation JU topic, the project selected under this Clean Hydrogen JU topic is expected to propose and pursue suitable alternative pathways to enable relevant integration and demonstration activities.

[2] https://www.clean-aviation.eu/research-and-innovation/clean-aviation/our-strategic-research-innovation-agenda

[3] https://cordis.europa.eu/project/id/101101381

[4] https://cordis.europa.eu/project/id/826247

[5] https://cordis.europa.eu/project/id/101101409

[6] https://cordis.europa.eu/project/id/101101404

[7] https://cordis.europa.eu/project/id/101140499

[8] https://cordis.europa.eu/project/id/101101967

[9] https://cordis.europa.eu/project/id/101140559

[10] https://cordis.europa.eu/project/id/101102003